Process for lubricating a bearing surface



Sept. 19, 1967 E. W. TURNS ET AL FROCESS FOR LUBRICATING A BEARING SURFACE Filed July 29, 1966 EARL W. TURNS JOHNNY W. HEAD HAROLD C.HOFFMAN ARTHUR C- PORTER INVENTORS MW/mama ATTORNEY United States Patent 3,342,703 PROCESS FOR LUBRICATING A BEARING SURFACE Earl W. Turns, Johnny W. Head, Harold C. Hoffman, and Arthur C. Porter, Fort Worth, T-ex., assignors to General Dynamics Corporation, Fort Worth, Tex., a corporation of Delaware Filed July 29, 1966, Ser. No. 568,804 2 Claims. (Cl. 204-32) ABSTRACT OF THE DISCLOSURE The process of applying metallic solid film lubricants by electro-deposition on a workpiece to assure a chemical bond therebetween, the lubricant having homogeneity and uniformity which includes preparation of the work surface as by chemical cleaning followed by roughening, followed by cleaning. The workpiece is then immersed in an electrolyte as the cathode, the electrolyte being a solu tion of potassium cyanide, potassium carbonate, and silver cyanide, and a soluble metal salt from the group consisting of rhenium or molybdenum, the deposition for the lubricant being from .0001 inch to .0015 inch.

This is a continuation-in-part of our copending application Ser. No. 274,413 filed Apr. 22, 1963, now abandoned, and relates generally to a process for lubricatinga base metal by the deposition of a solid film of metallic. lubricant thereon to provide a high pressurezhigh temperature-stable bearing surface.

More particularly the invention relates to a process for lubricating a bearing surface by electro-depositing alloys employing silver as the elemental constituent in combination with at least one alloying constituent of ductile metal, thus imparting to and plating such base metal with a durable solid lubricant coating.

. Electro-deposition of an alloy onto a base metal, per se, is? well known in the art. However, precise control made possible by employment of the present electro-deposition process for plating a workpiece with a solid film metallic lubricant is deemed to be novel, and with proper control of such. factors as current density, hydrogen ion concentration, temperatures, etc., makes possible the attainment of an effective solid metal film lubricant from the several aqueous plating solutions hereinafter described containing compounds of the respective alloying elements.

Prior known processes, in which metal matrices are utilized, inherently have, in common, at least three serious deleterious adjuncts. The first of these resides in the inability of the process to function efficiently in physical areas where accessibility is a problem. The second results from the difiiculty encountered in attempting to maintain sufficient process control to insure homogeneity and uniformity within the lubricant coating. The third adjunct is encountered in the fact that known processes by which conventional metal films are applied depend upon mechanical bonds to achieve adhesion of the film to the workpiece being plated, thus reducing its reliability. Another inherent objection to lubricants utilizing organic or inorganic binders arises from the processes for applying such binders and their reliance upon mechanical adhesion. Such binders limit the operable range and reliability of the lubricants as well as requiring considerable surface preparation and curing, thus increasing the need for additional manufacture control.

It is therefore an object of this invention to provide an improved process whereby metallic solid film lubricants may be applied to a workpiece by electro-deposition.

It is another object of the invention to provide a proc- Patented Sept. 19, 1967 piece and deposited alloy, whereby the electrons of theatoms of base metal and coating are shared, thus eliminating the binder and curing cycles required in conventional mechanical bonding.

It is still another object of the invention to provide a process which imparts homogeneity and uniformity within the applied lubricant.

It is a further object of this invention to provide a process of considerable flexibility in application, facilitating the depositing of the metallic lubricant to areas not readily accessible, while maintaining rigid manufacturing process controls.

Other objects and advantages of this invention will be apparent from the following description, illustration and appended claims, and the terms and expressions employed herein are in terms of description and not limitation, and no intention, in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof is intended, but recognizes that various modifications are possible within the scope of the invention claimed.

The figure illustrates one form of apparatus utilized as an integral portion of the herein described process.

Referring now to the figure, a glass, rubber or plastic lined tank 1 has disposed therein and contiguous with its inner cylindrical surface 2, an insoluble screen-like anode 3 of platinum or platinum cladl tantalum. The anode, or positive electrode of the DC circuit 3 is supported by one or more platinum wires 4, one of which is connected with direct current power supply 5; said power supply being either a motor generating type, or optionally of a rectifying type capable of varying potential and current, which can be suitably monitored. Cathode 6, the negative electrode of the D.C. circuit, is attached to the object workpiece 7 to which the lubricating compound is to be electro-deposited by a brass spring or similar other suitable clamp 8, making sure positive contact is effected, thus assuring uniform current distribution. Clamp 8 is of such construction and so placed that the workpiece 7 is not masked in critical areas. Homogeneity of the electrolytic solution 9 is virtually assured during electrolysis by agitation of the bath resultant from escaping hydrogen gas formed at the cathode; however, mechanical agitation assures complete homogeneity and can be accomplished conventionally or by placement of a magnet 10 in the bottom of tank 1. Tank 1 has, immediately adjacent its underside, a magnetic agitator 11 which creates a rotating magnetic field, facilitating movement of the magnet 10 through magnetic coupling.

In general, the process for applying lubricating alloys is divided into three separate phases; preparation of the surface to be plated, formulation of the electrolytic solution and subsequent electrolysis.

I The preparation of the surface of the object workpiece to be lubricated is normally preceded by all heat treating processes which may be required, after which it is chemically cleansed, as with methyl ethyl ketone, and subsequently grit-blasted with fine mesh aluminum oxide, for example No. commercial grade, to effect a surface roughness of 15 tion of dense microscopic irregularities in the surface to which the metal piece is then recleansed to remove all grit and petroleum films by dipping in methyl ethyl ketone or in other suitable solvents conventionally employed for this purpose.

oxides by immersion in any suitable chemical etchant to 30 R.M.S. This results in the formalubricant is to be applied. The Worki solution but preferably is anodically electrocleaned in, for example, an aqueous solution of sodium hydroxide and sodium cyanide.

Preparatory cleaning having been accomplished a base metal cathode or workpiece, such for example as T-l steel, upon which the metallic lubricant is to be electrodeposited, is immersed in an electro-chemical solution contained Within the apparatus hereinabove described; T-1 being the S.A.E. designation for the steel alloy: carhon-0.72%, chromium-4.0%, tungsten18.0%, and vanadium-1.0%. This generally exemplary electrolytic solution may contain, for example: potassium cyanide, KCN60 to 125 grams per liter; potassium carbonate, K CO 3 to 75 grams per liter; silver cyanide, AgCN, 3 to 7 grams per liter, with a suificient quantity of one of the soluble metal salts taken from a group consisting of rhenium or molybdenum to produce an ionic concentration capable of electro-depositing from 3 percent to 7 percent alloying element in a silver matrix.

For a first example, the ionic concentration obtained by the addition of, in the case of rhenium, of from .75 to 1.25 grams per liter of either sodium perrhenate, potassium perrhenate, or any of the alkali compatible rhenates and finally the addition of adequate distilled water to comprise one liter, is operably satisfactory. The temperature of the solution has an operable range of between 10 C. and 52 C.; the preferable range being between 23.8 C. and 26.6 C. or what is normally considered to be room temperature.

The electro-deposition is continued at a selected current density of about 1.0 amp per square decimeter to about 13.5 amps per square decimeter for from minutes to about 60 minutes, depending upon the solution or bath being employed, until the layer of metallic lubricant is deposited, this layer preferably having a thickness of from .0004 inch to .0008 inch, although layers between .0001 inch and .0015 inch have been shown to be within the critical range and are relatively satisfactory metallic lubricants for high pressurezhigh temperature bearing operations. For the electro-chemical solution hereinabove described a current density of 4.10 amps/dec. has been found to be optimum when applied for about 15 minutes.

In the preferred process, wherein, as the first example of an operative embodiment, a silver/rhenium alloy is to be deposited as a solid film metallic lubricant upon a base metal of S.A.E. T-l steel, the workpiece or base metal is first cleaned by immersion in a bath of methyl ethyl ketone to remove scale, dirt and other foreign matter. It is next degreased in a vapor bath of trichloroethylene and grit blasted with 120 to 140 mesh aluminum oxide powder. The workpiece is then given an anodic electrocleaning in an aqueous solution of one pound per gallon of sodium hydroxide and one pound per gallon of sodium cyanide. The anodic electro bath is operated at 67 C.- 82 C. and at 5-6 volts for 3 to 5 minutes. The piece is thereupon removed from the anodic electro-cleaning bath and the silver/rhenium alloy deposited thereon by immersing the workpiece in an aqueous solution consisting essentially of:

Grams per liter Silver cyanide 5 Sodium or potassium perrhenate 1 Potassium cyanide 75 Potassium carbonate 15 During deposition the solution is maintained substantially at room temperature or 218 C.26.6 C. with a current density of 4.10 amps. per square decimeter for a period of 15 minutes. The anodes employed are preferably of stainless steel, platinum or other suitable insoluble metals. This results in a deposition of the silver/rhenium on the T-l base metal to a thickness ranging from .0001 in. to .0015 in. This optimum range of thickness is functionally crtical in that any substantially greater thickness will cause the deposit to peel or spall under high loads at elevated temperatures and any substantially lesser thick- Silver cyanide 5 Sodium molybdate 1 Potassium cyanide 75 Potassium carbonate 15 The above solution is maintained substantially at room temperature of 23.8 C.26.6 C. during deposition, with a current density of 4.10 amps. per square decimeter for a period of about 15 minutes. The anodes employed are, as in example one, preferably of stainless steel, platinum or other suitable insoluble metals. This results in a deposition of silver/molybdenum on the base metal to a thickness ranging from .0001 in. to .0015 inch. However, again as in example one, a thickness of between .0004 in. to .0008 in. is generally sought for.

Presence of all aforementioned alloying elements has been established and was verified by the X-ray diffraction analytical method.

As thus described, the present invention encompasses a process for lubricating a bearing surface with a solid film lubricant ca able of cycling low-high-low temperatures while subjected to extremely high bearing pressures. In general, the process envisions electro-deposition of a silver/rhenium, or molybdenum lubricant having a homogeneous composition and which shares electrons with the lubricated element to achieve an exceptionally strong adhesion through molecular bonding, and obviating the use of binders and curing cycles typical of prior art solid film lubricants. This process employs surface preparation and subsequent deposition of the lubricant Within the critical ranges specified, thereby precluding peeling or spalling with resultant seizure on the one hand and excessive friction and resultant wear life vitiation on the other.

Having thus described the invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. A process for lubricating the bearing surface of a base metal, comprising:

(A) preparing the surface of the base metal for receiving a solid lubricant deposit,

(B) intimately adhering a bimetallic surface lubricant to the exposed surface of said base metal; said adherence of said bimetallic lubricant being effected by the steps of:

(1) electro-depositing a silver matrix alloy upon the exposed surface of the base metal to a thickness of from .0001 of an inch to about .0015 of an inch by immersing said base metal as cathode in an aqueous solution for from about 5 minutes to about 60 minutes at a current density of from about 1.0 amp. per square decimeter to about 13.5 amps. per square decimeter at a temperature of from about 10 C. to about 52 C.; said aqueous solution consisting essentially (a) potassium cyanide (KCN) from about 60 grams per liter to about grams per liter,

(b) potassium carbonate (K CO from about 3 grams per liter to about 75 grams per liter,

(c) silver cyanide (AgCN) from about 3 to about 7 grams per liter, and

(d) a soluble metal salt consisting of an alkali metal compatible rhenate salt from about .75 to about 1.25 grams per liter.

5 6 2. A process for lubricating the bearing surface of a grams per liter to about 125 grams per base metal, comprising: liter,

(A) preparing the surface of the base metal for re- (b) potassium carbonate (K CO from about ceiving a solid lubricant deposit, 3 grams per liter to about 75 grams per liter, (B) intimately adhering a bimetallic surface lubricant 5 (c) silver cyanide (AgCN) from about 3 to the exposed surface of said base metal; said adgrams 3 about 7 P llter, f herence of said bimetallic lubricant being effected a soluple Salt CQIISISUHE Of an alkall metal by the Steps compatlble sodium molybdate (Na MoO (1) eIectro-depositing a silver matrix alloy upon from about to about grams P hterthe CXIfJgSCd sugafle off the bagetmeltjal to g 10 References Cited ness mm. 0 an inc 0a out. o an inch by immersing said base metal as cathode g Modem Electroplatmg 90-93 in an aqueous solution for from about min- G h A utes to about 60 minutes at a cur-rent density of 15 5 1 1 2 3 5 lectroplatmg Engmeenng from about P Square declmeter to Field, Samuel: The Deposition of Gold-Silver Alloys,

about P P Square decimeter at 3 pp. 502-511, Transactions of The Faraday Society, vol. temperature of from about C. to about 52 1920..1921

C.; said aqueous solution essentially consisting of: JOHN H. MACK, Primary Examiner.

(a) potassium cyanide (KCN) from about G. KAPLAN, Assistant Examiner. 

1. A PROCESS FOR LUBRICATING THE BEARING SURFACE OF A BASE METAL, COMPRISING: (A) PREPARING THE SURFACE OF THE BASE METAL FOR RECEIVING A SOLID LUBRICANT DEPOSIT, (B) INTIMATELY ADHERING A BIMETALLIC SURFACE LUBRICANT TO THE EXPOSED SURFACE OF SAID BASE METAL; SAID ADHERENCE OF SAID BIMETALLIC LUBRICANT BEING EFFECTED BY THE STEPS OF: (1) ELECTRO-DEPOSITING A SILVER MATRIX ALLOY UPON THE EXPOSED SURFACE OF THE BASE METAL TO A THICKNESS OF FROM .001 OF AN INCH TO ABOUT .0015 OF AN INCH BY IMMERSING SAID BASE METAL AS CATHODE IN AN AQUEOUS SOLTUTION FOR FROM ABOUT 5 MINUTES TO ABOUT 60 MINUTES AT A CURRENT DENSITY OF FROM ABOUT 1.0 AMP. PER SQUARE DECIMETER TO ABOUT 13.5 AMPS. PER SQUARE DECIMETER AT A TEMPERATURE OF FROM ABOUT 10*C. TO ABOUT 52* C.; SAID AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF: (A) POTASSIUM CYANIDE (KCN) FROM ABOUT 60 GRAMS PER LITER TO ABOUT 125 GRAMS LITER, (B) POTASSIUM CARBONATE (K2CO3) FROM ABOUT 3 GRAMS PER LITER TO ABOUT 75 GRAMS PER LITER, (C) SILVER CYANIDE (AGCN) FROM ABOUT 3 TO ABOUT 7 GRAMS PER LITER, AND (D) A SOLUBLE METAL SALT CONSISTING OF AN ALKALI METAL COMPATIBLE RHENATE SALT FROM ABOUT .75 TO ABOUT 1.25 GRAMS PER LITER.
 2. A PROCESS FOR LUBRICATING THE BEARING SURFACE OF A BASE METAL, COMPRISING: (A) PREPARING THE SURFACE OF THE BASE METAL OR RERECIVING A SOLID LUBRICANT DEPOSIT. (B) INTIMATELY ADHERING A BIMETALLIC SURFACE LUBRICANT TO THE EXPOSED SURFACE OF SAID BASE METAL; SAID ADHERENCE OF SAID BIMETALLIC LUBRICANT BEING EFFECTED BY THE STEPS OF: (1) ELECTRO-DEPOSITING A SILVER MATRIX ALLOY UPON THE EXPOSED SURFACE OF THE BASE METAL TO A THICKNESS OF FROM .001 OF AN INCH TO ABOUT .0015 OF AN INCH BY IMMERSING SAID BASE METAL AS CATHODE IN AN AQUEOUS SOLTUION FOR FROM ABOUT 5 MINUTES TO ABOUT 60 MINUTES AT A CURRENT DENSITY OF FROM ABOUT 1.0 AMP. PER SQUARE DECIMETER TO ABOUT 13.5 AMPS. PER SQUARE DECIMETER AT A TEMPERATURE FROM ABOUT 10*C. TO ABOUT 52* C.; SAID AQUEOUS SOLUTION ESSENTIALLY CONSISTING OF: (A) POTASSIUM CYANIDE (KCN) FROM AB OUT 60 GRAMS PER LITER TO ABOUT 15 GRAMS PER LITER, (B) POTASIUM CARBONATE (K2CO3) FROM ABOUT 3 GRAMS PER LITER TO ABOUT 75 GRAMS PER LITER. (C) SILVER CYANIDE (AGCN) FROM ABOUT 3 GRAMS TO ABOUT 7 GRAMS PER LITER, AND (D) A SOLUBLE SALT CONSISTING OF AN ALKALI METAL COMPATIBLE SODIUM MOLYBDATE (NA2MOO4) FROM ABOUT .75 TO ABOUT 1.25 GRAMS PER LITER. 